Fifth-wheel trailers are generally large, high profile trailers. They are typically coupled to a lead vehicle, such as a pick-up or flat-bed truck, by a fifth-wheel connector assembly mounted on a frame within the bed of the truck so that the fifth-wheel connector is disposed in a plane above that of the bed of the truck. Most such couplers are secured to the bed of the truck. Such permanent attachment of the coupler is problematic when the truck bed is needed for other purposes, such as cargo loading or camper carrying. A typical coupled hitch is not desirable since the connector assembly and frame usually take up a significant amount of space. Moreover, the removal of the assembly and frame from the truck bed typically requires an inordinate amount of time and effort.
Previous efforts to provide a mechanism for coupling allow a fifth wheel to be attached to a ball-hitch, such as a goose-neck hitch disposed at the rear of a tow vehicle, or in the bed of a pick-up or flat-bed truck, in order to avoid the use of a fifth wheel hitch utilizing a significant amount of space in the bed of the tow vehicle. Examples of such adaptors include those disclosed in U.S. Pat. Nos. 5,240,740, 6,024,372, 6,416,073 and 6,776,431, the disclosures of which are incorporated by reference herein. Typically, each of these devices consists of a top structure for connecting to a fifth wheel trailer, a frame extending downwards from the top structure, and a bottom structure for attaching to a ball hitch. While the frames may have a height adjustment, since they are simply metal boxes, these adaptors do not compensate for load conditions or road conditions, which can create discomfort for the driver and passenger when towing and place unnecessary wear and tear on the components.
U.S. Pat. No. 5,785,341, which is incorporated by reference herein, discloses a pneumatic isolator for use in attaching a trailer to a tow vehicle. An airspring is vertically mounted atop a tube extending down to the attachment hitch. The airspring compensates for the up and down motion of the trailer and tow vehicle as the tube slides in an outer tube. A single external shock absorber is used to connect the inner tube to the outer tube and to compensate for the reverse motion of the airspring. Although this design compensates for up and down motion, it does not adequately compensate for forward, reverse or lateral forces acting on the hitch during towing. It also requires permanent attachment to the fifth wheel trailer, preventing the fifth wheel trailer from being used with a standard fifth wheel hitch.
As such, an improved fifth-wheel hitch adaptor that enables a fifth wheel trailer to be attached to a retractable kingpin located in the bed of a tow vehicle (or attached to a hidden coupler mounted under the tow vehicle bed) and that compensates for forces from multiple directions during towing would be an improvement in the art. Such an adaptor that was releasably attachable would be a further improvement in the art.